Method For Culturing Benthic Organisms Without Feeding

ABSTRACT

A method for culturing benthic organisms in a culture pond without feeding uses an apparatus for continuously drawing up bottom layer water and dispersing it into upper layer water. The apparatus is provided for a culture pond of benthic organisms. Organic matter in the bottom layer water is mixed with the upper layer water to be mineralized, thereby raising the density of inorganic nutrient salts, so that photosynthesis in the upper layer water is activated to increase plant plankton.

TECHNICAL FIELD

The present invention relates to a method for culturing benthicorganisms without feeding.

BACKGROUND ART

One method commonly used nowadays for culturing shrimps in a culturepond formed on land is a high-density culturing method wherein pelletsmade of animal material are fed to shrimps to harvest 500 g/m² ofshrimps every year. In this method, water in the culture pond iscirculated along the periphery of the pond to gather sludge composed ofexuviae of shrimps, excreta of shrimps, etc. to the center area of thepond, and then divers go under water to dredge the bottom of the centerarea of the pond, thereby removing the sludge gathered there.

Drawbacks of the high-density culturing method include that the cost offeed puts a burden on producers because it accounts for half of theculturing cost, sludge removed from the culture pond causesenvironmental problems, etc. On the other hand, a careless culturingmethod wherein open seawater is let in and out a culture pond to cultureshrimps without feeding is very low in harvest and makes the culturingbusiness financially difficult.

DISCLOSURE OF INVENTION

The present invention was made to solve the aforementioned problems.Therefore, the object of the present invention is to provide a methodfor culturing shrimps, wherein cost of feed is lower than that of thehigh-density culturing method, accumulation of sludge is restricted, andharvest is higher than that of the careless culturing method.

Another object of the present invention is to provide a method forculturing benthic organisms other than shrimps, such as shellfishes,squillas, sea slugs, clam worms, etc., wherein cost of feed is low,accumulation of sludge is restricted, and harvest is higher than that ofthe careless culturing method.

In order to achieve the aforementioned objects, the present inventionprovides a method for culturing benthic organisms without feedingcomprising steps of, providing a culture pond of benthic organisms withan apparatus comprising means for continuously drawing up bottom layerwater and means for dispersing the drawn up water into upper layerwater, and mixing organic matter in the bottom layer water with theupper layer water to mineralize it, thereby raising the density ofinorganic nutrient salts in the upper layer water to activatephotosynthesis in the upper layer water, thereby increasing plantplankton in the upper layer water.

Continuous dispersion of bottom layer water into upper layer watercauses dispersion of organic matter, such as exuviae of benthicorganisms, excreta of benthic organisms, etc., which are suspended inthe bottom layer water, into the upper layer water. Aerobic bacteriaincrease in the upper layer water containing high density dissolvedoxygen to decompose the organic matter coming from the bottom of theculture pond into inorganic nutrient salts. The density of inorganicnutrient salts in the upper layer water increases to activatephotosynthesis, thereby increasing plant plankton and animal planktoneating plant plankton. Benthic organisms grow and proliferate, supportedby the abundant plant plankton and animal plankton available for theirconsumption.

In accordance with the present invention, cost of feed becomes zerobecause benthic organisms can be cultured without feeding. In accordancewith the present invention, a culture pond for culturing benthicorganisms can be continuously used for many years because accumulationof sludge on the bottom of the pond is restricted. Though the method ofthe present invention results in a harvest poorer than that of thehigh-density culturing method, it achieves a harvest better than that ofthe careless culturing method. In accordance with the present invention,wholesome and tasty benthic organisms can be produced because plantplankton and animal plankton like those eaten by natural benthicorganisms are consumed by cultured benthic organisms.

In a preferred embodiment of the present invention, the method furthercomprises a step of fertilizing the bottom of the culture pond withorganic matter before starting the culture to supply the upper layerwater with inorganic nutrient salts at the beginning stage of theculture of the benthic organisms.

The density of organic matter in the bottom layer water is low at thebeginning stage of the culture of the benthic organisms. Fertilizing thebottom of the culture pond with organic matter such as poultry excreta,etc. before the start of the culture can establish a high density ofinorganic nutrient salts in the upper layer water to increase plantplankton and animal plankton at the beginning stage of the culture. Thefertilization causes only a slight increase of culturing cost becauseone time fertilization before the start of the culture is usuallyenough.

In another preferred embodiment of the present invention, the methodfurther comprises a step of fertilizing the bottom of the culture pondwith organic matter during the culture.

The bottom of the culture pond can be fertilized with organic matterduring the culture when the proliferation of the plant plankton and theanimal plankton is insufficient.

In another preferred embodiment of the present invention, the methodfurther comprises a step of continuously exchanging seawater in theculture pond with open seawater using a water exchange pump to keep thetemperature and quality of seawater in the culture pond in goodcondition.

Continuous exchange of seawater in the culture pond with open seawaterusing a water exchange pump can prevent degradation of the quality ofseawater in the culture pond with the passage of time and preventtemperature rise of the seawater in the culture pond with the passage oftime.

In another preferred embodiment of the present invention, the methodfurther comprises a step of excavating the bottom of the culture pondbelow the apparatus to form a bottom layer water reservoir.

Organic matter in the water near the bottom of the culture pond can bemade to gather in the bottom layer water reservoir so as to be drawn upefficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a structural view of a system for carrying out a method forculturing shrimps without feeding in accordance with a preferredembodiment of the present invention. (a) is a plan view and (b) is asectional view.

FIG. 2 is a sectional view of a density current dispersion apparatus forcarrying out a method for culturing shrimps without feeding inaccordance with a preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment, wherein the present invention is used forculturing shrimps, which are kinds of benthic organisms, will bedescribed.

As shown in FIG. 1, a shrimp culture pond 1 is located beside a beach L.The shrimp culture pond 1 is provided with a density current dispersionapparatus 2 at the center portion. A water exchange pump 3 is placed onthe sea-bottom near the beach L. An intake pipe 4 extends from the waterexchange pump 3 across a bank of the beach to the shrimp culture pond 1.A discharge pipe 5 distanced from the intake pipe 4 extends from theshrimp culture pond 1 to a place near the beach L, penetrating slightlydownward through the bank of the beach on the way.

As shown in FIG. 2, the density current dispersion apparatus 2 comprisesa floating structure 21 immersed in the water. The floating structure 21comprises an upper compartment 21 a, a middle compartment 21 b and alower compartment 21 c.

A bottom layer water intake pipe 22 penetrates the center portion of thelower compartment 21 c as seen from above to extend downward vertically.The upper end of the bottom layer water intake pipe 22 communicates withthe middle compartment 21 b. The lower end of the bottom layer waterintake pipe 22 is located near the bottom surface of the shrimp culturepond 1. The bottom layer water intake pipe 22 is provided with a pump 23at the portion thereof extending through the lower compartment 21 c.

An upper layer water intake pipe 24 penetrates the center portion of theupper compartment 21 a as seen from above to extend upward verticallybeyond the water surface WL of the shrimp culture pond 1. The upper endof the upper layer water intake pipe 24 is closed. The upper layer waterintake pipe 24 is provided with a plurality of intake ports 24 a at theportion below and near the water surface. The lower end of the upperlayer water intake pipe 24 communicates with the middle compartment 21b. The upper layer water intake pipe 24 is provided with a pump 25 atthe portion thereof extending through the upper compartment 21 a.

A plurality of outlet passages 26 circumferentially distanced from eachother extend radially and horizontally from the circumferential wall ofthe middle compartment 21 b. The outlet passages 26 are located at thelower portion of upper layer of seawater in the shrimp culture pond 1.

The density current dispersion apparatus 2 is suspended in the seawaterin the shrimp culture pond 1 and is moored at the center portion of theshrimp culture pond 1 with anchor cables 27 provided with anchors.

Electric cables for supplying the pumps 23 and 25 with electric power,which are not shown in Figures, extend from the pumps to an electricpower supply located near the shrimp culture pond 1.

A method for culturing shrimps without feeding in accordance a preferredembodiment of the present invention is carried out as follows using theaforementioned equipment.

The pump 23 of the density current dispersion apparatus 2 operates tocontinuously draw up bottom layer water in the shrimp culture pond 1through the bottom layer water intake pipe 22, thereby discharging thewater in the middle compartment 21 b of the floating structure 21. Thepump 25 operates to continuously draw upper layer water in the shrimpculture pond 1 through the upper layer water intake pipe 24, therebydischarging the water in the middle compartment 21 b of the floatingstructure 21.

The bottom layer water is mixed with the upper layer water in the middlecompartment 21 b. The mixed water is discharged through the outletpassages 26 into the lower portion of the upper layer of the seawater inthe shrimp culture pond 1. The lower portion of the upper layer of theseawater in the shrimp culture pond 1 has the same temperature as themixed water. The upper layer water is stratified according to itsdensity. The mixed water penetrates one of the layers of the stratifiedupper layer water, said one of the layers having the same density as themixed water, to disperse horizontally to a great distance, while forminga current of seawater with a uniform density distribution, i.e., adensity current.

Continuous dispersion of the bottom layer water into the upper layerwater causes dispersion of organic matter, such as exuviae of shrimps,excreta of shrimps, etc., which are suspended in the bottom layer water,into the upper layer water. Aerobic bacteria increase in the upper layerwater containing high density dissolved oxygen to decompose the organicmatter coming from the bottom of the culture pond into inorganicnutrient salts. The density of the inorganic nutrient salts in the upperlayer water increases to activate photosynthesis, thereby increasingplant plankton and animal plankton eating plant plankton. Shrimps growand proliferate, supported by abundant plant plankton and animalplankton available for their consumption. Sludge accumulation on thebottom of the culture pond is restricted because the organic matter inthe bottom layer water is transferred to the upper layer water anddecomposed there.

In accordance with the present embodiment, cost of feed becomes zerobecause shrimps can be cultured without feeding. The shrimp culture pond1 can be continuously used for many years because accumulation of sludgeon the bottom of the culture pond is restricted. Though the harvestbecomes poorer than that achieved by the high-density culturing method,the harvest becomes better than that achieved by the careless culturingmethod. Wholesome and tasty shrimps can be produced because plantplankton and animal plankton like those eaten by natural shrimps areconsumed by cultured shrimps.

In the present embodiment, the bottom of the shrimp culture pond 1 isfertilized with organic matter, such as poultry excreta, etc., beforestarting the culture to supply inorganic nutrient salts at the beginningstage of the culture of shrimps.

The density of organic matter in the bottom layer water is low at thebeginning stage of the culture of the shrimps because the quantity ofexuviae of shrimps, excreta of shrimps, etc., which are suspended in thebottom layer water, is small at the beginning stage of the culture ofshrimps. Fertilizing the bottom of the culture pond 1 with organicmatter before the start of the culture can establish a high density oforganic matter in the bottom layer water and a high density of inorganicnutrient salts in the upper layer water to increase plant plankton andanimal plankton at the beginning stage of the culture. The fertilizationcauses only a slight increase of culturing cost because one timefertilization before the start of the culture is usually enough.

The bottom of the shrimp culture pond 1 can be fertilized with organicmatter during the culture when the increase of the plant plankton andthe animal plankton is insufficient.

In the present embodiment, the water exchange pump 3 operates tocontinuously supply the shrimp culture pond 1 with open seawater throughintake pipe 4. Surface layer water in the shrimp culture pond 1 iscontinuously and naturally discharged to the open sea through thedischarge pipe 5.

Continuous exchange of seawater in the shrimp culture pond 1 withseawater in the open sea can prevent degradation of the quality of theseawater in the shrimp culture pond 1 with the passage of time andprevent temperature rise of the seawater in the shrimp culture pond 1with the passage of time.

Instead of continuously exchanging seawater in the shrimp culture pond 1with seawater in the open sea, it is possible to open and close afloodgate synchronously with ebb and flow of seawater in the open sea,thereby regularly exchanging seawater in the shrimp culture pond 1 withseawater in the open sea.

As indicated by an alternate long and short dash line in FIG. 1, thebottom of the shrimp culture pond below the density current dispersionapparatus 2 can be excavated to form a bottom layer water reservoir 6.Organic matter in the water near the bottom of the culture pond can bemade to gather in the bottom layer water reservoir 6 to be drawn upefficiently. When the bottom layer water reservoir 6 is fertilized withorganic matter before the start of the culture, the organic matter canbe dispersed into the upper layer water efficiently.

The present invention can be used for culturing benthic organisms otherthan shrimps, such as shellfishes, squillas, sea slugs, clam worms, etc.The harvest becomes better than that achieved by the careless culturingmethod, while minimizing cost of feed and restricting accumulation ofsludge.

INDUSTRIAL APPLICABILITY

The present invention can be widely used for culturing benthicorganisms, such as shrimps, shellfishes, squillas, sea slugs, clamworms, etc.

1. A method for culturing benthic organisms without feeding comprisingsteps of, providing a culture pond of benthic organisms with anapparatus comprising means for continuously drawing up bottom layerwater and means for dispersing the drawn up water into upper layerwater, and mixing organic matter in the bottom layer water with theupper layer water to mineralize it, thereby raising the density ofinorganic nutrient salts in the upper layer water to activatephotosynthesis in the upper layer water, thereby increasing plantplankton in the upper layer water.
 2. A method for culturing benthicorganisms without feeding of claim 1, further comprising a step offertilizing the bottom of the culture pond with organic matter beforestarting the culture to supply the upper layer water with inorganicnutrient salts at the beginning stage of the culture of the benthicorganisms.
 3. A method for culturing benthic organisms without feedingof claim 1, further comprising a step of fertilizing the bottom of theculture pond with organic matter during the culture.
 4. A method forculturing benthic organisms without feeding of claim 1, furthercomprising a step of continuously exchanging seawater in the culturepond with open seawater using a water exchange pump to keep thetemperature and quality of seawater in the culture pond in goodcondition.
 5. A method for culturing benthic organisms without feedingof claim 1, further comprising a step of excavating the bottom of theculture pond below the apparatus to form a bottom layer water reservoir.6. A method for culturing benthic organisms without feeding of claim 2,further comprising a step of fertilizing the bottom of the culture pondwith organic matter during the culture.